Braun tube for producing television images of large size



March 22, 1938. K. SCHLESINGER ,9

BRAUN TUBE FOR PRODUCING TELEVISION IMAGES OF LARGE SIZE Filed June 11, 1934 4 A i s E I I f k5 6 l4 7WBW up/5 Jnveniok:

Patented Mar. 22, 1938 UNITED STATES PATENT OFFICE BRAUN TUBE FOR PRODUCING TELEVISION IMAGES OF LARGE SIZE In G 1 Claim.

It is known that in Braun tubes having two pairs of deflecting plates a mutually disturbing action takes place between the pairs of deflecting plates.

It has already been proposed by the applicant for the purpose of avoiding these disturbing effects to space the pairs of deflecting plates widely apart, to provide screening means between the pairs of plates, and/or to screen ofi the leads against each other.

The proposed measures, taken singly or in their entirety, have been found to be suificient so long as the size of image does not appreciably exceed a certain size (approximately 9 x 12 cm. or also 10 x 15 cm.).

It has been found, however, that these measures are not fully adequate for the production of television images of large size, and that in the case of large images of this nature the known trapezoid defect is not to be wholly eliminated by reason of the same.

The subject matter of the invention is a Braun tube of large size, for instance more than 9 x 12 cm., having a picture receiving screen, which permits of the production of large images of exactly rectangular form.

According to the invention, the first deflection (for example image deflection) is performed by the use of deflecting coils, and the second deflection (for example line deflection) by the use of deflecting plates.

The use of deflecting coils for the image deflection is possible without difficulty owing to the slow image-change frequency (for example, 25-50 periods).

Since the magnetic and the electrostatic fields do not in the present case interfere with each other, it is possible according to the invention to avoid completely the trapezoid defect, and to produce entirely rectangular images of large size.

Further, the use of the mixed deflection permits of avoiding the influence of the deflecting field upon the breaking field of the electron-optical system, which otherwiseespecially in tubes of the high vacuum type-is very dimcult to be avoided.

A tube according to the invention is illustrated by Way of example in the drawing. In the same:

I is the bulb, 2 the fluorescent screen, 3 the deflecting coil for the image deflection and 4 the deflecting plates for the line deflection. The distance between the plates 4 and the image screen is made to be such that on the latter there are produced television images of large size (for ermany June 27, 1933 example, larger than 10 x 15 cm.). This distance may amount, for example, to 20-30 cm. or more. 5 is an electrode acting as electron return flow intercepter, and 6 a metallic wall coating. The wall coating 6 may conveniently be linked up with anode potential, whilst the ring 5 may possess a potential which is positive in relation to the anode. 'l is the cathode, 8 the control electrode. 9 shows a metallic diaphragm acting as the first anode, said diaphragm being provided with the opening. 12 which is focussed on to the picture receiving screen by means of an electron-optical system comprising the electrodes l0 and II.

Further, means are provided for supplying the deflecting plates with a deflecting voltage of one frequency; and means for supplying the deflecting coils with a deflecting voltage of another frequency. Such means are generally known in the art and are indicated in the drawing by M, resp. I3.

Means for supplying the metallic coating with the anode potential and means for supplying the auxiliary electrode 5 with a potential, which is higher than the anode potential, are indicated at l5.

The provision of the two auxiliary electrodes 5 and 6 is of particular importance in the case of the Braun tube according to the invention which is preferably operated under high vacuumas a rounding oif may occur if an auxiliary field of this nature is not provided.

I claim:

In a television cathode ray tube the combination with a picture receiving screen having an area of at least 10 times 15 centimetres, of a pic-- ture area scanning system comprising a pair of deflecting plates adapted tobe supplied with a deflecting voltage of one frequency for deflecting the cathode ray in one direction and a pair of deflecting coils adapted to be supplied with a deflecting voltage of another frequency for defleeting the cathode ray'in another direction vertical to the first said one, of an auxiliary electrode mounted between said scanning system and said screen and adapted to be supplied with a potential lying above anode potential, and of a metallic coating applied to the wall of the cathode ray tube, said coating beginning near said auxiliary electrode and projecting for at least 8 centimetres in the direction towards said screen, said coating being adapted to be supplied with anode potential.

KURT SCI-HESINGER. 

